Genome-wide screen reveals important roles for ESCRT proteins in drug/ion resistance of fission yeast.

To study sodium homeostasis, we performed a genome-wide screen for deletion strains that show resistance to NaCl. We identified 34 NaCl-resistant strains. Among them, the largest group that consists of 10 genes related to membrane trafficking and 7 out of 10 genes are ESCRT proteins which are involved in cargo transportation into luminal vesicles within the multivesicular body. All of the ESCRT related mutants which showed sodium resistance also showed defects in vacuole fusion. To further understand the role of the ESCRT pathway in various ion homeostasis, we examined sensitivity of these ESCRT mutants to various cation salts other than NaCl, including KCl, LiCl, CaCl2, CoCl2, MgCl2, NiSO4 and MnCl2. While these ESCRT mutants showed resistance to LiCl, CoCl2 and MgCl2, they showed sensitivity to KCl, CaCl2, NiSO4 and MnCl2. Then we examined sensitivity of these ESCRT mutants to various drugs which are known to inhibit the growth of fission yeast cells. While these ESCRT mutants were more or equally sensitive to most of the drugs tested as compared to the wild-type cells, they showed resistance to some drugs such as tamoxifen, fluorouracil and amiodarone. These results suggest that the ESCRT pathway plays important roles in drug/ion resistance of fission yeast.